Add environment variable to control connection heartbeat

[ppietruszewski-consult-red]

This patch introduces a new environment variable, RABBITMQ_HEARTBEAT_SECONDS, that controls the timing of channel heartbeat. Previously, when generating bundles took more time than set in the default heartbeat value, the bundle generator had no chance of returning a successful message due to channel closure despite successfully generating the bundle. By setting the RABBITMQ_HEARTBEAT_SECONDS environment variable, we can ensure that the channel remains open until the bundle generation is complete, thus allowing the generator to return a successful message.

Note: The default value of heartbeat that is set when environment variable is unset (60 seconds) is taken from the Pika documentation.

[CLAassistant]

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